1. Field of the Invention
The present invention relates to a tool head.
2. Description of the Prior Art
Hand tool or power tool can fasten or unfasten a fastener quickly and is effort-saving. A tool head is used to fasten or unfasten the fastener. Generally, the tool head may be a flat tool head, Phillips tool head, hexagonal tool head, ball-shaped tool head or Torx tool head, and is exchangeably connected to a driving end of a driving tool. However, the tool head may be broadly considered to include socket. To avoid disengagement of the socket from the fastener, the socket is generally provided with a magnetic member on the inner surface thereof, or with a structure which includes an elastic abutting member disposed in an opening on the inner surface and an elastic annular member disposed around the socket, so as to engage with the fastener. As to the flat tool head, Phillips tool head, hexagonal tool head, ball-shaped tool head or Torx tool head which has a small size, the working end thereof is too thin to allow arrangement of the magnetic member or the elastic abutting member. TWM460727 is directed to an extension rod provided with a magnetic member or elastic abutting member; however, it cannot avoid disengagement of the fastener from the tool head.
DE 4416268 is directed to a hexagonal wrench and U.S. Pat. No. 6,302,001 is directed to a ball-shaped tool head. In DE 4416268 or U.S. Pat. No. 6,302,001, a working end is formed with an annular groove and an O-ring is received in the annular groove, wherein the O-ring is partially protrusive outside the annular groove to avoid disengagement of a fastener from the tool head. However, there will exist disadvantages as recited below.
1. The working end has a smallest diameter at the portion that is formed with the annular groove, and this will affect the application of force of the tool head.
2. For receiving the O-ring, the annular groove has an opening width greater than the diameter of a cross section of the O-ring, so that the O-ring can move slightly and the O-ring is possible to disengage from the annular groove during insertion of the working end into a fastener, which cannot avoid disengagement of a fastener from the tool head.
3. In U.S. Pat. No. 6,302,001, an annular groove is formed along a portion which has the largest diameter of the ball-shaped tool head having plural ramps. The largest diameter of the ball-shaped tool head is smaller than the width of an insertion recess of a fastener, and the O-ring is a little protrusive outside the annular groove. This structure would not affect the application of force to the fastener when the ball-shaped tool head is perpendicularly inserted into the insertion recess; however, it does affect the application of force to the fastener when the ball-shaped tool head is non-perpendicularly inserted into the insertion recess since the O-ring just very slightly contact the inner surface of the insertion recess and is very slightly deformed to engage with the inner surface of the insertion recess, and thus the fastener can disengage from the tool head easily.
4. The tool head of U.S. Pat. No. 5,259,280 is provided with particles of friction material consisting of metallic or mineral material so as to avoid disengagement of a fastener from the tool head. However, to facilitate insertion of the tool head into an insertion recess of a fastener without affect of the particles, the thickness of the tool head has to be reduced, thus degrading the structural strength and output torque of the tool head. In structure of U.S. Pat. No. 6,883,405, a workpiece engagement surface is irradiated over a large area and/or locally with a high level of energy, such that a region of an irradiated zone which is close to the surface melts and solidifies suddenly at an edge to form a rib, so as to increase the friction of the tool head and a fastener to avoid disengagement of the fastener from the tool head. However, it is complicated and difficult to form the rib at the edge of the small-sized tool head, and the solidified rib is rigid and undeformable. Furthermore, the structure of U.S. Pat. No. 6,883,405 has defects of poor structural strength and lower output torque.
As to a small-sized tool head having size identification mark, it is not easy to recognize the size just via the size identification mark, especially in a dark environment. Thereupon, the middle body of a tool head would be colored in black, electroplated or spray-coated, such as disclosed in TWM457613 and TWM437766. To provide identification, some kind of tool head is formed with plural annular grooves, and plural colored rings are received in the annular grooves of the tool head, such as disclosed in TWM434656; some kind of tool head is formed with colored protrusion(s), such as disclosed in I358347.
The above-mentioned structures have complicated production process and high production cost. The structures provided with colored rings or protrusion(s) can be recognized only in a bright environment but difficult to be recognized in a dark environment. Generally, for small-sized tool head (especially slotted or Phillips tool head), it is still a hard issue that how to provide a tool head which can avoid disengagement of the fastener from the tool head and has identification effect, without degrading the structural strength of the working end and without any additional process and cost tool head.
The present invention is, therefore, arisen to obviate or at least mitigate the above mentioned disadvantages.